Each year, 51,200 people in the United States are diagnosed with bladder cancer and 10,600 die of the disease. Exposure to environmental chemicals as well as genetic factors play a significant role in initiation of bladder cancer. Epidemiologic investigations have clearly shown an increased risk of bladder and other cancers associated with arsenic exposure, but the level at which it poses a measurable health risk has been the topic of considerable debate, and its precise mechanism of action remains unknown. Furthermore, a number of studies have reported an interaction between smoking, genetic polymorphisms and cancer risk. We will test the hypothesis that polymorphisms in the nucleotide excision repair pathway are associated with increased bladder cancer risk. We will address this hypothesis using exposure data and blood samples collected in a large population-based study of bladder cancer in the New Hampshire (850 cases, 1,365 controls). The specific aims of the project will be to 1) test the hypothesis that genetic variants in the nucleotide excision repair pathway genes (XPD, XPC, XPA, and ERCC1), are associated with increased risk of bladder cancer, and 2) determine whether environmental exposures (arsenic, smoking) and nucleotide excision repair polymorphisms interact to increase bladder cancer risk. This study presents a unique opportunity to clarify how genetic and environmental factors affect DNA repair and contribute to bladder cancer susceptibility. Through our study, we hope to contribute to both our mechanistic understanding of bladder cancer and to identify subgroups of the population that may be at greater risk of environmentally-induced cancers.